Method to produce electrically isolated or insulated areas in a metal, and a product comprising such area

ABSTRACT

The present specification relates to a method to produce electrically isolated or insulated areas in a metal, and a product comprising such area. The method according to the invention comprising the steps of: providing a metallic structure; performing a plasma electrolytic oxidation and/or anodization process such that an oxide layer is achieved on an area of the metallic structure; and electrically isolating a part of the metallic structure by removing part of the metallic structure and/or connecting a further metallic structure to the metallic structure with the oxide layer.

CROSS REFERENCE TO RELATED APPLICATIONS

The present specification is a National Phase Entry of InternationalApplication No. PCT/NL2016/050372 filed 25 May 2016 and entitled “Methodto produce electrically isolated or insulated areas in a metal, and aproduct comprising such area” which, itself, claims priority to NL2014857 filed 26 May 2015 and entitled “Method to produce electricallyisolated or insulated areas in a metal, and a product comprising sucharea,” each of which are incorporated by reference herein in theirentireties.

FIELD

The present specification relates to a method to produce electricallyisolated or insulated areas in a metal. Such areas are used in variousapplications, including electronic devices. More specifically, themethod according to the present specification relates to forming metalstructures that have an electrically isolated area that is connected bynon-conductive part(s). In this context isolating and insulating bothdescribe the electrical separation of an area from other parts and canbe used alternately in the context of the present specification.

BACKGROUND

A problem with conventional electronic devices, including computingdevices such as mobile phones, tablets, computers, laptops etc., thatuse an antenna is that the devices often cover the antenna with ahousing, thereby increasing the risk of hindering communication and/orproducing noise.

SUMMARY

The present specification has for its object to improve conventionalproducts having an electrically isolated area.

This object is achieved with the method to produce electrically isolatedareas in a metal, the method comprising the steps of:

providing a metallic structure;performing a plasma electrolytic oxidation and/or anodization processsuch that an oxide layer is achieved on an area of the metallicstructure; andelectrically isolating a part of the metallic structure by removing partof the metallic structure and/or connecting a further metallic structureto the metallic structure with the oxide layer.

The treated structure can be used in various applications, includingelectronic devices. More specifically, the method according to thepresent specification relates to forming metal structures that have anelectrically isolated area that is connected by non-conductive part(s).Such structure can advantageously be used as an antenna or antenna part,such as an RF antenna. Such antenna that is produced involving themethod according to the present specification enables improvedcommunication having less noise, for example.

In embodiments according to the present specification the ceramic layerhas a thickness in the range of 5-300 μm, preferably 10-200 μtm, morepreferably 15-150 μm and most preferably a thickness is about 100 μm.

By providing the ceramic layer with a sufficient thickness the stabilityand strength of the heater is improved. Furthermore, the insulation isincreased, enabling control of heat transfer and/or heat production. Thethickness of the ceramic layer is adapted to the desiredcharacteristics. This flexibility during production provides a furtheradvantage of the system according to the present specification.

In embodiments according to the present specification, the ceramic layeris provided on or at the conductor with plasma electrolytic oxidation(PEO).

Principles of a PEO process are disclosed in WO 2011/010914 and areincluded by reference herein. In embodiments, the element is made froman aluminium material, or other suitable material, such as titanium, onwhich a porous metal oxide layer, such as aluminium oxide or titaniumoxide, is grown with plasma electrolytic oxidation. In this embodimentof the present specification the metal oxide layer is provided on a sideof the metal layer involving a plasma oxidation process, morespecifically a plasma electrolytic oxidation process. By performing aplasma electrolytic oxidation process on the first metal layer locallythe electric brake down potential of the oxide film on the metal layeris exceeded and discharges occur. Such discharges lead to a type oflocal plasma reactors, resulting in a growing oxide. This builds thedesired structure for the membrane layer. The plasma electrolyticoxidation process creates very fine pores in the metal layer, therebyforming an oxide layer that contains small pores. This method provides aceramic layer that can be made efficiently. Surprisingly, also the poresizes of this ceramic layer can be controlled more effectively and thedesired characteristics for such ceramic layer can be achieved moreaccurately. A further advantage of the method according to the presentspecification is that it enables the manufacturing of ceramic materialin a modular way. Optionally, this enables providing complicatedthree-dimensional shapes of the desired element.

Plasma electrolytic oxidation enables that a relatively thick aluminium,titanium or other suitable metal layer is grown from the metal (>130 μm)by oxidizing (part of) the metal to metal oxide. Especially the use oftitanium provides good results. The resulting layer is a porous,flexible and elastic metal oxide ceramic. Plasma electrolytic oxidation(>350 550 V) requires much higher voltage compared to standard anodizing(15-21 V). At this high voltage, micro discharge arcs appear on thesurface of the aluminium, or other material, and cause the growth of thethick (metal) oxide layer. Results have shown that a ceramic layer canbe achieved on an aluminium foil of about 13 μm thickness, with aflexible and elastic ceramic layer. One of the advantageous effects ofusing plasma electrolytic oxidation to provide the ceramic layer is thatdue to the growth of the layer from the metal during oxidation theadherence of the ceramic layer to the metal is excellent.

Alternative manufacturing methods for producing an electrically isolatedarea in a metal include sintering or spark plasma sintering, oxidationof the surface layer of the metal by heating in oxygen rich environment,anodizing, and plasma spraying. Also, it would be possible to deposit analuminium, or other material, coating on the conductor of the heaterelement, for example with arc spraying, and to oxidize the depositedmaterial to an oxide with plasma electrolytic oxidation.

As an alternative to PEO, or in combination therewith, an anodizationprocess may be applied to provide a ceramic layer. Typically,anodization takes place at a voltage that from 1 to 300 V DC, althoughmost fall in the range of 15 to 21 V. Higher voltages are typicallyrequired for thicker coatings formed in sulfuric and organic acid.Typically, the current that is applied is in the range from 30 to 300amperes/meter².

The resulting ceramic layer may have pores with a diameter in the rangeof 1-150 nm in diameter on the interface of the metal/ceramic layer andpores with a diameter in the range of 50 nm to 5 μm on the outside. Theceramic layer thickness can range from under 0.5 μm up to 150 μm forarchitectural applications.

In embodiments of the present specification the method comprises thestep of electrically isolating a part of the metallic structure byremoving part of the metallic structure. This provides separateparts/elements in the metallic structure that are electrically isolated.

Alternatively, or in combination therewith, the method in anotherembodiment of the present specification comprises the step of connectinga further metallic structure to the metallic structure with the oxidelayer. Because of the process conditions, involving high temperaturesand pressure, the metal oxide layer melts during plasma oxidation andsolidifies again during cooling. Provided the further metallic structureis positioned closed to the metallic structure the oxide layers of therespective structure will solidify together, thereby connecting themetallic structures, while preferably electrically isolating themetallic structures.

In embodiments of the present specification the method further comprisesthe step of masking parts of the metallic structure and performing theplasma electrolytic oxidation and/or anodization such that an oxidelayer is achieved on an unmasked area of the metallic structure. Thisprovides an effective method to provide a structure or an isolatingstructure to the metallic structure.

Removing part of the metallic structure may be performed afterperforming the plasma electrolytic oxidation process. This enableseffective oxidation. In embodiments, removing part of the metallicstructure comprises performing an etching process, for example chemicaletching or electrochemical etching.

In embodiments the etching involves electrochemical etching.

Electrochemical etching, also referred to as electrochemical machining(ECM) and, in embodiments, including jet electrochemical machining(JET-ECM), allows for a precise, fast and reproducible local removal ofmaterial of the first metal layer. Surprisingly, in this etching processit was found that etching the first metal layer does not significantlyinfluence the metal oxide layer. In fact, the metal oxide layer remainssubstantially intact whereas the metal is locally etched away. Thisenables an efficient and effective manufacturing of a product comprisingan electrically isolated area, for example. Performing the removing stepafter producing the oxide layer further improves the electric isolationof the respective area. For example, this may prevent or reduceundesired bulging and/or oxidation to the sides in a transversaldirection. This improves the quality of the resulting product. Also,this may further reduce the noise disturbance. As a further advantagethe etching process that is applied may automatically stop when reachingthe oxide layer. This improves the isolation that is effectivelyprovided.

In embodiments the method further comprises the step of providingnon-conductive material to the removed areas of the metallic structures.

The use of non-conductive material further improves the quality of theresulting product. In embodiments according to the present specificationthe method further comprises the step of increasing the stability and/orstrength of the metallic structure by providing a stability layer on theoxide layer of the metallic structure after performing the plasmaelectrolytic oxidation and/or anodization process.

By providing a stability layer the strength and stability of themetallic structure is significantly improved. This improves the etchingperformance. In embodiments, the stability layer comprisesnon-conductive material, for example an epoxy.

In embodiments with a stability layer, the stability layer is providedwith a thickness in the range of 10 to 100 μm, preferably in the rangeof 20 to 75 μm, and most preferably with a thickness of about 50 μm. Itwas shown that such thickness improves stability and strength therebyenabling or improving possibilities for further processing, such aselectrochemical etching.

In embodiments according to the present specification the method furthercomprises the step of removing the stability layer.

Optionally, the stability layer is removed after performing the etchingprocess. This may depend on the actual use or application of theproduct.

In further embodiments of the present specification the method furthercomprises the step of providing a third metallic structure connectingthe other metallic structures together. In embodiments, such thirdmetallic structure will connect the two other metallic structurestogether in a plasma oxidation process. Optionally, at least one of thetwo, three of further metallic structures is of a different material.For example, in one of the embodiments the third metallic structure is asacrificial metallic structure that can be used to connect the othermetallic structures. An example of such embodiment is the use of atitanium structure as third, sacrificial structure for connecting twoaluminum structures. In a further example, metallic structures ofaluminum, magnesium and titanium are connected together.

The present specification also relates to a product according to thepresent specification, with the product comprising an electricallyisolated area that is produced with a method as described earlier.

The product provides the same effects and advantages as described forthe method.

In embodiments, such product is a computing device, such as mobilephones, tablets, computers, laptops etc., and the area is part of anantenna. In embodiments, the effects of undesired noise in thecommunication can be significantly reduced. The product may havedifferent shapes or configurations. For example, the metallic structuresof the product may comprise a tubular shape, a metallic mesh structureon the metallic structure, or a wire shape.

BRIEF DESCRIPTION OF THE DRAWINGS

Further advantages, features and details of the present specificationare elucidated on the basis of preferred embodiments thereof whereinreference is made to the accompanying drawings, in which:

FIG. 1 shows a cell and metal that is subjected to plasma oxidationaccording to the present specification;

FIG. 2 shows a cross section of the product resulting from the methodaccording to the present specification;

FIG. 3 shows a top view of the product shown in FIG. 2;

FIG. 4 shows a process according to an embodiment of the presentspecification with a stability layer; and

FIG. 5A-D shows different embodiments of the present specification withtwo or more metallic structures.

DETAILED DESCRIPTION

A piece of metal 2 (FIG. 1) is subjected to plasma oxidation to createan oxide layer 4 on a metal plate. In order to make a ceramic layer onone side of the metal and on a particular region, the metal is placed ina plasma electrolytic oxidation cell 6 as shown in FIG. 1.

The metal plate 2 preferably aluminum is connected to an anode.Alternative materials titanium, magnesium or other so called valvemetals can also be used. The synthetic material 8 shown in the figurecan be a hard plastic which can be compressed against another hardplastic with in between a metal plate 2 and a rubber 10 for sealing.This synthetic material 8 acts as a masking material to form plasmaelectrolytic oxide 4 at unmasked areas 12. Different kind of shapes canbe used to mask the metal plate 2.

The rubber material 10 seals the cell and masks the metal 2. Thesynthetic material 8 also acts as a mask. In such a cell 6 as describedhere only the part 12 which is not masked is treated through plasmaelectrolytic oxidation. Plasma electrolytic oxidation (PEO) or micro arcoxidation creates a non-conductive metal oxide layer 4 on the metalplate 2. Different properties, like color of the layer, can be adjustedby choosing different electrolytes for the PEO process. Electrolytesthat can be used contain KOH (potassium hydroxide) in a concentrationrange 0-10 g/l, and Na₂SiO₃ 5H₂O concentration range 0-10 g/l, forexample. It is known from literature that these electrolytes or mixturesof these electrolytes can give a good PEO layer on Aluminum. Also othersalts can be used like Na₂AlO₂ or Na₂SiF₆ (NaPO₃)₆, potassium borateK₂B₄O₇, or sodium borate Na₂B₄O. It will be understood that otheralternatives could also be envisaged in accordance with the presentspecification.

In an illustrated embodiment of the present specification the structureof the metal element 2 comprises a thin plate or sheet of titanium,aluminium, or any other valve metal, such as magnesium, zirconium, zinc,niobium, vanadium, hafnium, tantalum, molybdenum, tungsten, antimony,bismuth, or an alloy of one or more of the preceding metals. Plate orsheet 2 is coated on the other side through plasma electrolyticoxidation. Plasma electrolytic oxidation is done by placing titaniumplate or sheet 2 in an electrolyte. For example, the electrolytecomprises 15 g/l (NaPO₃)₆ and 8 g/l Na₂SiO₃.5H₂O. The electrolyte ismaintained at a temperature of 25° C. through cooling. Plate or sheet 2is used as an anode and placed in a container containing theelectrolyte. Around plate or sheet 2 a stainless steel cathode 12 ispositioned. A current density is maintained between the plate or sheetand cathode 22 of about 0.15 A/cm². The current is applied in a pulsedmode of about 1000 Hz. The current increases rapidly to about 500 Voltbetween the plate or sheet and cathode 22. This creates a plasmaelectrolytic oxidation process on anode plate or sheet 2 and createsceramic layer 4. It will be understood that process parameters maydepend on the structure of the plate or sheet and/or the dimensionsthereof.

After the PEO process a ceramic layer 4 is obtained with a layerthickness that depends on the treatment time. In order to obtain parts14 which are electrically isolated from the metal 2, the metal 14remaining attached to the ceramic layer 4 has to be removed. There aremany methods which can remove the metal. Electrochemical machining isvery effective in removing the metal 14 under the oxide layer 4.

After the plasma oxidation treatment the metal plate was transferred toan etch cell. In this cell the metal was etched via electrochemicalmachining. The plate was mounted in this cell with the metal side facingthe cathode. This cathode consists partly of a metal and a plastic. Themetal shape of the cathode determines the shape and dimensions whichwill be etched in the metal plate. A pulsed electric field is appliedbetween the cathode and the anode (metal plate with on the other sidethe metal oxide layer). A highly conductive electrolytic flow wasprovided between the anode and the cathode. The potential differencebetween the anode and the cathode was in the beginning 1-15 Volts andincreased gradually during the etching. The potential increases sharplywhen the metal is etched away and reaches the metal oxide layer. Thenthe process was stopped. The current density was kept at a value ofabout 250 kA/m². This process results in a metal plate with on one sidea metal oxide layer and a structure etched in the metal. Fluids can befiltrated through the open structure in the metal. The metal oxide layercan be supported during filtration by a metal plate and/or a (paper)filter that is optionally provided in between the metal oxide layer andthe metal plate. Because the surface roughness of the metal oxide layeris high the permeate water can flow easily away to the sides and can beseparated from the feed water. This filtration configuration also allowsfor high filtration pressures over 5 bars.

Tests have shown that a combination of the PEO process withelectrochemical machining achieves a high quality product, for examplewith very accurate removal of the metal at the desired spots.

After performing the plasma oxidation (PEO) step, or if the process isperformed at lower potentials after the anodization step, part of themetal 14 can be removed from the other side by electrochemicalmachining, for example. The advantage of electrochemical machining isthat the process stops when it reaches the non-conductive ceramic layer4. The formed opening can be filled with a non-conductive polymer 16 orother substances. By doing so, electrically isolated areas 18 arecreated.

A cross section of a product 20 formed this way is shown in FIG. 2. Atop view of product 20 may look like as shown in FIG. 3.

In embodiments according to the present specification manufacturingprocess 102 (FIG. 4) starts with providing metal plate of sheet 104.With a PEO process, or alternatively an anodization process, ceramiclayer 106 is provided on one side of metal element 104. Stability layer108 may be provided on and/or in ceramic layer 106 to improve stabilityand strength of element 104 with ceramic layer 106. In the illustratedembodiment stability layer 108 is from epoxy. In the next step an ECMprocess is performed that provides grooves, holes or openings 110 fromthe other side of element 104. The ECM process is stopped as grooves,holes or openings 110 reach ceramic layer 106. Optionally, grooves,holes or openings 110 are filled with non-conductive material 112, forexample epoxy. Also optionally, stability later 108 can be removed fromceramic layer 106.

In connecting method 202 according to an embodiment of the presentspecification (FIG. 5A) metallic structure 204 is connected to secondmetallic structure 206 with plasma electrolytic oxidation bondingmetallic structures 204, 206 together with the oxide layers. Inembodiments, the connection is made such that metallic structures 204,206 are electrically isolated. Optionally, in an alternative method 208(FIG. 5B) two metallic structures 210, 212 are connected withsacrificial third metallic structure 214. For example, the respectivematerials for metallic structures 210, 212 and 214 are aluminum,magnesium and titanium. Alternatively, middle structure 214 is oftitanium and the other structures 210, 212 are of aluminum.

The structures can be shaped as plates or sheets. Alternatively, othershapes are possible. For example, in process 216 (FIG. 5C) two tubularmetallic structures 218, 220 are connected. Such shape may act asantenna, for example. In a further process 222 (FIG. 5D) of the presentspecification mesh 224 (or alternatively a wire) is connected toplate/sheet 226 (or alternatively a wire). Also, two or more wires maybe connected. It will be understood that also other embodiments, shapesor configurations can be envisaged in accordance with the presentspecification.

All different kind of shapes can be made on the metal by plasmaelectrolytic oxidation and masking the metal during plasma oxidation andremoving the metal after plasma oxidation by electrochemical machiningand filling the cavity with a nonconductive material.

The present specification is by no means limited to the above describedpreferred embodiments thereof. The rights sought are defined by thefollowing claims, within the scope of which many modifications can beenvisaged.

1. A method to produce an electrically isolated area in a metal,comprising the steps of: providing a metallic structure; performing aplasma electrolytic oxidation and/or anodization process such that anoxide layer is achieved on an area of the metallic structure; andelectrically isolating a part of the metallic structure by removing partof the metallic structure and/or connecting a further metallic structureto the metallic structure with the oxide layer.
 2. The method accordingto claim 1, further comprising the step of masking parts of the metallicstructure and performing the plasma electrolytic oxidation and/oranodization such that an oxide layer is achieved on an unmasked area ofthe metallic structure.
 3. The method according to claim 1, whereinremoving part of the metallic structure is performed after performingthe plasma electrolytic oxidation process and/or anodization process. 4.The method according to claim 3, wherein removing part of the metallicstructure comprises performing an etching process.
 5. The methodaccording to claim 4, wherein the etching process comprises anelectrochemical etching process.
 6. The method according to claim 4,wherein the etching process comprises the step of automatically stoppingthe etching when reaching the oxide layer.
 7. The method according toclaim 1, further comprising the step of providing non-conductivematerial to the removed part or parts of the metallic structure.
 8. Themethod according to claim 1, further comprising the step of increasingthe stability and/or strength of the metallic structure by providing astability layer on the oxide layer of the metallic structure afterperforming the plasma electrolytic oxidation and/or anodization process.9. The method according to claim 8, wherein the stability layercomprises non-conductive material.
 10. The method according to claim 8,wherein providing a stability layer comprises providing a layer with athickness in the range of 10 to 100 μm, preferably in the range of 20 to75 μm, and most preferably with a thickness of about 50 μm.
 11. Themethod according to claim 8, further comprising the step of removing thestability layer.
 12. The method according to one claim 1, furthercomprising the step of providing a third metallic structure connectingthe other metallic structures together.
 13. The method to claim 1,wherein at least one of the metallic structures is of a differentmaterial.
 14. A product comprising an electrically isolated area that isproduced with a method according to claim
 1. 15. The product accordingto claim 14, wherein the product is a computing device and the area ispart of an antenna.
 16. The product according to claim 14, wherein themetallic structures of the product comprise a tubular shape, a metallicmesh structure on the metallic structure, or a wire shape.
 17. Theproduct according to claim 15, wherein the metallic structures of theproduct comprise a tubular shape, a metallic mesh structure on themetallic structure, or a wire shape.
 18. The method according to claim2, wherein removing part of the metallic structure is performed afterperforming the plasma electrolytic oxidation process and/or anodizationprocess.
 19. The method according to claim 18, wherein removing part ofthe metallic structure comprises performing an etching process.
 20. Themethod according to claim 19, wherein the etching process comprises anelectrochemical etching process.
 21. The method according to claim 20,wherein the etching process comprises the step of automatically stoppingthe etching when reaching the oxide layer.